The invention relates generally to computer system storage and more particularly to mechanisms (methods and devices) for providing distributed computer system storage.
It is common for organizations to employ large numbers of computers for tasks such as data storage. Typically, some or all of an organization's computers may be interconnected to form a network whereby two computer systems are interconnected so that they are capable of exchanging information. With the adoption of computer network technology came the desire for increased storage capacity. Increased storage capacity, in turn, led to a need to distribute filesystems across networked computers. In general, distribution of file systems is done by software applications that keep track of files stored across a network. One goal of distributing filesystems is to allow a user/application of one computer (or node) in a computer network to access data or an application stored on another node in the computer network. Another goal of distributing file systems is to make this access transparent with respect to the stored object's physical location.
FIG. 1 shows a computer system employing distributed file system technology in accordance with the prior art. As shown, node-A 100 and node-B 102 are interconnected by communication link 104. Illustrative nodes include specialized or general purpose workstations and personal computers. An illustrative communication link employs coaxial or twisted pair cable and the transport control protocol (TCP). Each node A and B executes a local version of a distributed filesystem, 106 and 108 respectively. Each distributed filesystem manages the storage of objects to/from a storage unit (e.g., 110 and 112), each of which may include one or more storage devices. Illustrative storage devices include magnetic disks (fixed, floppy, and removable) and optical media such as CD-ROM disks.
One well known distributed file system is the Network File System (NFS®) from Sun Microsystems, Incorporated of Palo Alto, Calif. In NFS, a server node may make its filesystem (in part or in whole) shareable through a process known as “exporting.” A client node may gain access to an exported file system through a process known as “mounting.” Exporting entails specifying those filesystems, or parts thereof, that are to be made available to other nodes (typically through NFS map files). Mounting adds exported filesystems to the file structure of a client node at a specified location. Together, the processes of exporting and importing define the filesystem namespace.
For example, consider FIG. 2 in which node 200 has local filesystem 202 including directories X, Y, and Z, and node 204 has local filesystem 206 including directories α, β, and γ. If node 204 exports, and node 200 imports filesystem 206 (often referred to as cross-mounting), node 200 may have combined system namespace 208. From directory structure 208, a user/application on node 200 may access any data object in remote directories α, β, and γ as if α, β, and γ were local directories such as X or Y.
One significant feature of distributed storage such as that illustrated in FIG. 2, is that all references to an object stored in directory a by a user at node 200 (i.e., through combined filesystem namespace 208) are resolved by the filesystem local to and executing on node 204. That is, the translation of an object's reference to the physical location of that object is performed by the file system executing on node 204. Another significant feature of current distributed file systems such as NFS® is that the processes of exporting and importing must be performed for each new directory to be shared. Yet another significant feature of current distributed file systems is that shared storage (e.g., mount points α, β, and γ) appear as discrete volumes or nodes in filesystem namespace. In other words, an exported filesystem (or part thereof) appears as a discrete objects of storage in the namespace of each importing node. Thus, system namespace is fragmented across multiple storage nodes. To export a single directory from a node to all other nodes in a computer network, not only must the exporting node's map of objects (or its equivalent) be updated to specify the directory being exported, but every node wanting to import that directory must have its map of objects updated. This may happen frequently as, for example, when additional storage is added via a new storage node being attached to the network, and requires significant administrative overhead for each such occurrence.
Thus, it would be beneficial to provide a distributed storage mechanism that reduces administrative overhead associated with sharing memory and unifies the shared system namespace.